Pad conditioner dresser

ABSTRACT

Methods for extending the service life of a CMP pad dresser having a substrate and a plurality of superabrasive particles disposed thereon which is used to dress a CMP pad are disclosed and described. The method may include dressing the chemical mechanical polishing pad with the dresser; determining superabrasive particle wear by measuring a mechanical property of the pad, dresser, or combination thereof; and responding to the mechanical property measurement by varying pressure and RPM between the pad and the dresser in relation to the superabrasive particle wear in order to extend dresser life. Additionally, a method may include dressing the chemical mechanical polishing pad with the dresser; vibrating, in a direction substantially parallel to a working surface of the pad, a member selected from the pad, the dresser, a wafer being polished by the pad, or any combination thereof, to minimize a mechanical stress on the pad, dresser, wafer, or combination thereof.

FIELD OF THE INVENTION

The present invention relates generally to methods for dressing orconditioning a chemical mechanical polishing (CMP) pad. Accordingly, thepresent invention involves the chemical and material science fields.

BACKGROUND OF THE INVENTION

Chemical mechanical polishing (CMP) is an effective planarizationprocess utilized in the semiconductor industry for manufacturing wafersof ceramic, silicon, glass, quartz, and metals, including the processesof inter-level dielectric (ILD) and Damascene metallization. Suchpolishing processes generally entail applying the wafer against arotating pad made from a durable organic substance such as polyurethane.A slurry containing a chemical capable of breaking down the wafersubstance is introduced onto the pad. The slurry additionally containsabrasive particles which act to physically erode the wafer surface. Theslurry is continually added to the spinning CMP pad, and the dualchemical and mechanical forces exerted on the wafer cause it to bepolished in a desired manner.

Of particular importance to the quality of polishing achieved, is thedistribution of the abrasive particles across the surface of the pad.The top of the pad holds the particles, usually by a mechanism such asfibers, or small pores, which provide a friction force sufficient toprevent the particles from being thrown off of the pad due to thecentrifugal force exerted by the pad's spinning motion. Therefore, it isimportant to keep the top of the pad as flexible as possible, to keepthe fibers as erect as possible, and to assure that there are anabundance of open pores available to receive new abrasive particles.

One problem with maintaining the top of the pad results from anaccumulation of debris from the work piece and the abrasive slurry. Thisaccumulation causes a “glazing” or hardening of the top of the pad, andcauses the fibers to mat down, thus making the pad less able to hold newabrasive particles from the ongoing slurry flow. This situationsignificantly decreases the pad's overall polishing performance.Therefore, attempts have been made to revive the top of the pad by“combing” or “cutting” it with various devices. This process has come tobe known as “dressing” or “conditioning” the CMP pad. Many types ofdevices and processes have been used for this purpose. One such deviceis a dresser disk with a plurality of superabrasive particles, such asdiamond, attached to a surface or substrate.

New dresser disks have sharp superabrasive particles that cut dense,deep asperities into the CMP pad surface. The slurry is effectively heldin these deep asperities, resulting in a high polishing rate of thewafer. Through continued use, however, the superabrasive particles inthe dresser disk begin to wear, and their tips begin to gradually dull.The dull superabrasive particles do not penetrate into the CMP padsurface as deeply and the cutting grooves becomes wider as thesuperabrasive particle tips wear down. This wearing effect results inasperities that are wide, sparse, and shallow. CMP pads conditioned withsuch a dresser disk can no longer effectively hold the slurry, therebydecreasing the polishing rate of the wafer. Superabrasive particles onthe dresser disk will continue to wear until they are pressing into thepad without cutting. Also, less effective cutting by the dresser diskcauses debris to collect on the CMP pad surface, resulting in unevenpolishing and increased wafer scratching.

In view of the foregoing, methods of using and constructing CMP paddresser disks that achieve superior dressing results, with maximizedefficiency and lifespan continue to be sought.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method for extending theuseful service life of a chemical mechanical polishing pad dresser usedto dress a chemical mechanical polishing pad, the dresser having asubstrate and a plurality of superabrasive particles disposed thereon.Such a method may include dressing the chemical mechanical polishing padwith the dresser; determining superabrasive particle wear by measuring amechanical property of the pad, dresser, or combination thereof; andresponding to the mechanical property measurement by varying pressureand RPM between the pad and the dresser in relation to the superabrasiveparticle wear in order to extend dresser life.

In another embodiment, the method may include dressing the chemicalmechanical polishing pad with the dresser; vibrating, in a directionsubstantially parallel to a working surface of the pad, a memberselected from the pad, the dresser, a wafer being polished by the pad,or any combination thereof, to minimize a mechanical stress on the pad,dresser, wafer, or combination thereof; and varying the pressure and RPMbetween the pad and the dresser, including gradually increasing thepressure and/or the RPM between the pad and the dresser in a non-linearmanner over time as the dresser is used, such that the dresser life isextended, wherein the pressure and the RPM is increased when thechemical mechanical polishing pad surface exhibits wear.

There has thus been outlined, rather broadly, various features of theinvention so that the detailed description thereof that follows may bebetter understood, and so that the present contribution to the art maybe better appreciated. Other features of the present invention willbecome clearer from the following detailed description of the invention,taken with the accompanying claims, or may be learned by the practice ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of superabrasive particle showing little wear;

FIG. 2 is a photograph of a superabrasive particle showing some wear;

FIG. 3 is a illustrative diagram showing superabrasive particles anddescribing potential cutting patterns generated by the superabrasiveparticles according to an embodiment of the present invention; and

FIG. 4 is a graph depicting an example of polishing rate and defectcount over time according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present methods are disclosed and described, it is to beunderstood that this invention is not limited to the particular processsteps and materials disclosed herein, but is extended to equivalentsthereof as would be recognized by those ordinarily skilled in therelevant arts. It should also be understood that terminology employedherein is used for the purpose of describing particular embodiments onlyand is not intended to be limiting.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to an “abrasive particle” or a “pad” includes reference to oneor more of such abrasive particles or pad.

Definitions

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set forthbelow.

As used herein, “superabrasive particle,” “abrasive particle,” “grit,”or similar phrases mean any super hard crystalline, or polycrystallinesubstance, or mixture of substances, and include, but are not limitedto, diamond, polycrystalline diamond (PCD), cubic boron nitride (CBN),and polycrystalline cubic boron nitride (PCBN). Further, the terms“superabrasive particle,” “abrasive particle,” “grit,” “diamond,”“polycrystalline diamond,” “cubic boron nitride,” and “polycrystallinecubic boron nitride,” may be used interchangeably.

As used herein, “super hard” and “superabrasive” may be usedinterchangeably, and refer to a crystalline, or polycrystallinematerial, or mixture of such materials having a Vicker's hardness ofabout 4000 Kg/mm² or greater. Such materials may include withoutlimitation, diamond, and cubic boron nitride (cBN), as well as othermaterials known to those skilled in the art. While superabrasivematerials are very inert and thus difficult to form chemical bonds with,it is known that certain reactive elements, such as chromium andtitanium are capable of chemically reacting with superabrasive materialsat certain temperatures.

As used herein, “substrate” means the base portion of a CMP dresserhaving a surface on which the abrasive particles may be affixed. Thebase portion may be any shape, thickness, or material, and includes butis not limited to metals, alloys, ceramics, and mixtures thereof.

As used herein, “working surface” means the surface of a CMP pad dresserthat, during operation, faces toward, or comes in contact with a CMPpad.

As used herein, “leading edge” means the edge of a CMP pad dresser thatis a frontal edge based on the direction that the CMP pad is moving, orthe direction that the pad is moving, or both. Notably, in some aspects,the leading edge may be considered to encompass not only the areaspecifically at the edge of a dresser, but may also include portions ofthe dresser which extend slightly inward from the actual edge. In oneaspect, the leading edge may be located along an outer edge of the CMPpad dresser. In another aspect, the CMP pad dresser may be configuredwith a pattern of abrasive particles that provides at least oneeffective leading edge on a central or inner portion of the CMP paddresser working surface. In other words, a central or inner portion ofthe dresser may be configured to provide a functional effect similar tothat of a leading edge on the outer edge of the dresser.

As used herein, “sharp portion” means any narrow apex to which a crystalmay come, including but not limited to corners, ridges, edges, obelisks,and other protrusions.

As used herein, “pressure” refers to the applied force between a CMP paddresser and a CMP pad. Thus reference to increasing or decreasingpressure refers to variations in the applied force between the dresserand the pad that causes an increase or decrease in pressure.

As used herein, “RPM” refers to the relative motion as measured inrevolutions per minute between the CMP pad and the CMP dresser during adressing operation. As such, it is contemplated herewith that one orboth of the pad and dresser may by in motion. Thus reference toincreasing or decreasing RPM refers to variations in the applied forcebetween the dresser and the pad that causes an increase or decrease inRPM.

As used herein, “dressing operation” refers to a period when the dresseris pressing against and actively dressing the pad.

As used herein, “vibrate” means to oscillate an object in asubstantially horizontal direction, back and forth or from side to side,in a rapid movement. Vibrations may be continuous, intermittent,continuously variable, in accordance with a vibrational program, etc.Accordingly, a CMP pad, CMP pad dresser, wafer, or superabrasiveparticles of a CMP pad dresser can be vibrated at a desired frequency toobtain an optimal polishing performance.

As used herein, “ultrasonic” means any energy wave that vibrates withfrequencies higher than those audible to the human ear. For example suchfrequencies are higher frequencies than about 15,000 Hz, or in otherwords more than about 15,000 cycles per second.

As used herein, “substantially” when used in reference to a quantity oramount of a material, or a specific characteristic thereof, refers to anamount that is sufficient to provide an effect that the material orcharacteristic was intended to provide. The exact degree of deviationallowable may in some cases depend on the specific context.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc.

This same principle applies to ranges reciting only one numerical value.Furthermore, such an interpretation should apply regardless of thebreadth of the range or the characteristics being described.

The Invention

As previously discussed, CMP pad dressers are used to dress CMP pads inorder to remove dirt and debris, and to restore asperities in thesurface of the pad. Asperities are important to the function of the CMPpad, as they hold and channel slurry across the material being polished.Higher rates of polishing may be achieved when the CMP contains deep,dense asperities to hold the slurry. Sharp superabrasive particles suchas diamond, as shown in FIG. 1, are able to cut such optimal asperitiesin the CMP pad that maximize retention of the slurry, and thus provide ahigh rate of polishing. As the dresser is used, the embeddedsuperabrasive particles begin to wear over time, and their tips andedges become dull and rounded as shown in FIG. 2. Worn superabrasiveparticles cut less effectively into the CMP pad, resulting in a padsurface with asperities that are shallow, wider, and sparse. FIG. 3 is adiagrammatic representation that illustrates superabrasive particle wearand the subsequent effects on cutting patterns in the CMP pad. Assuperabrasive particles wear, cutting patterns of the dresser changes.Sharp superabrasive particles 10 cut deep asperities 12 in the surfaceof the CMP pad 14. As the superabrasive particles begin to wear 16,moderately deep asperities 18 are cut into the CMP pad surface 14. Whensuperabrasive particles become significantly worn 20, very shallowasperities 22 are cut, if at all. The superabrasive particles eventuallybecome so worn that they can no longer cut and/or clean, but merely rubagainst the pad surface. The surface of the pad becomes hard and coveredwith debris, increasing the rate of scratching and damage to the waferor other work surface. As such, the polishing rate of the CMP pad willdecline over time as the superabrasive particles wear. As shown in FIG.4, as the service life of the CMP pad dresser increases (time), thepolishing rate 30 decreases and the defect count 32 increases (FIG. 4).

The inventor has discovered that by varying the force applied to the CMPpad by the CMP pad dresser in relation to the level of wear of thesuperabrasive particles of the dresser, the service life of the dressercan be extended. For example, increasing the force between the CMP paddresser and the CMP pad as the superabrasive particles wear leads to anincrease in the service life of the dresser. By increasing the pressureand/or RPM, superabrasive particles press more deeply into the pad andthus cutting efficiency is increased. Additionally, such an increase inpressure and/or RPM will also allow a greater proportion of thesuperabrasive particles to come into contact with the pad surface.Superabrasive particles that do not protrude as far from the surface ofthe dresser can contact and dress the pad under increased pressureand/or RPM. Such an increase in pressure and/or RPM may be implementedbefore the superabrasive particles are completely worn, as significantlyworn superabrasive particles tend to facilitate damage to the wafer.Accordingly, in one aspect a method for extending the service life of aCMP pad dresser having a substrate and a plurality of superabrasiveparticles disposed thereon when used to dress a CMP pad is provided. Themethod may further include dressing the chemical mechanical polishingpad with the dresser; determining superabrasive particle wear bymeasuring a mechanical property of the pad, dresser, or combinationthereof; and responding to the mechanical property measurement byvarying pressure and RPM between the pad and the dresser in relation tothe superabrasive particle wear in order to extend dresser life.

Current practices tend to apply the dresser to the CMP pad with a fixedpressure, often about 10 lbs throughout the life of the dresser, as wellas RPM. Similarly, current dressing machines can only apply a fixedpressure and require that the machine be stopped in order for thepressure to be reset. Conversely, aspects of the present inventioncontemplate increasing the pressure and/or RPM between the CMP pad andthe dresser as a result of actual or anticipated wear of the associatedsuperabrasive particles. By increasing these applied forces, thesuperabrasive particle tips can cut deeper into the CMP pad surfacewhile the superabrasive particles are still in a condition to cut.Without wishing to be bound by theory, it is believed that increasingthe pressure and/or RPM in relation to superabrasive particle wear mayincrease the service life of the tool because the increased pressureand/or RPM may offset such wear. It should be noted that an increase ofthe applied forces is most effective if accomplished prior to thesuperabrasive particles becoming too dull to penetrate the pad,regardless of the amount of pressure applied. The extent of the increasein pressure and/or RPM or applied force can readily be determined by oneskilled in the art from examining the cutting pattern, examining thesuperabrasive particles, making estimations of superabrasive particlewear, etc. The amount of applied forces will also be dependent on thedresser size, dresser machine specifications, and the type of polishingbeing performed. Given such variations, a simple range of how much tovary the pressure and/or RPM is not practical. One of ordinary skill inthe art can, however, readily determine the necessary variations inpressure and/or RPM for a particular polishing process once inpossession of the present disclosure. In one specific aspect, however,the pressure and/or RPM between the CMP pad and the CMP pad dresser maybe increased by from about 1% to about 100%. In another specific aspect,the pressure and/or RPM may be increased by from about 1% to about 50%.In yet another specific aspect, the pressure and/or RPM may be increasedby from about 1% to about 20%. In a further specific aspect, thepressure and/or RPM may be increased by from about 1% to about 10%. Inanother further specific aspect, the pressure and/or RPM may beincreased by less than about 5%. In yet a further aspect the pressureand/or RPM may be increased by greater than about 100%.

It should also be understood that varying the pressure and/or RPM mayalso include decreasing the pressure and/or RPM, particularly for thosedressers with superabrasive particles exhibiting little or no wear.Sharp superabrasive particles often cut more deeply into the CMP padthan is required to hold the slurry. Such “overdressing” causes thesuperabrasive particles to wear more quickly. By decreasing the pressureand/or RPM between the pad and the dresser when the superabrasiveparticles are sharp, overall wear of the particles may be reduced, andthe service life of the dresser can be further extended.

The timing and extent of the increase in pressure and/or RPM between theCMP pad dresser and the CMP pad may be facilitated by making adetermination of superabrasive particle wear. Various methods ofdetermining superabrasive particle wear are contemplated, all of whichare considered to be within the scope of the present invention. Such adetermination may be an actual determination or an estimation based oncalculated or assumed wear patterns. Accordingly, as it is determinedthat superabrasive wear is occurring or has occurred, the applied forceor pressure and/or RPM between the CMP pad dresser and the CMP pad maybe varied accordingly in order to maintain more optimal asperityconfigurations in the surface of the CMP pad such as depth, width,density, etc.

In one aspect of the present invention, a determination of the extent ofsuperabrasive particle wear may include an examination of a dressed CMPpad surface. The depth, width, density, etc., of the asperities cut intothe CMP pad surface can give one skilled in the art some indication ofthe extent of the wear of the superabrasive particles. One advantage ofthis examination method is the ability to estimate superabrasiveparticle wear without the need of removing the dresser from thepolishing apparatus. Such examination can occur manually through visualobservation with or without a magnification apparatus, or by other meansof ascertaining the CMP pad surface texture. Examination can also occurautomatically through visual imaging or mechanical measuring processes.

In another aspect of the present invention, as discussed above,determining superabrasive particle wear can be performed by measuring amechanical property of the pad, dresser, or combination thereof. Themeasured mechanical property can be selected from the group consistingof factional force, acoustic emission, temperature, pad reflectivity,pad flexibility, pad elasticity, and combinations thereof. As such, inone aspect the measured mechanical property can be factional force. Inanother aspect, the measured mechanical property can be acousticemission. In another aspect, the measured mechanical property can betemperature. In another aspect, the measured mechanical property can bepad reflectivity. In another aspect, the measured mechanical propertycan be pad flexibility. In another aspect, the measured mechanicalproperty can be pad elasticity.

Virtually any aspect of the pattern of asperities can be utilized toevaluate the extent of superabrasive particle wear and thus trigger avariation in pressure and/or RPM. By improving at least onecharacteristic of the pattern of asperities by varying the cuttingpressure and/or RPM, slurry can be more effectively held on the surfaceof the CMP pad and more evenly distributed, polishing rate may beimproved, and the service life of the dresser will be increased. In oneaspect, the pressure and/or RPM may be increased when the CMP padsurface exhibits a decrease in average asperity density. Such a decreasein density may occur due to an increase in width, a decrease in length,etc. It may also be a result of ineffective cutting by the superabrasiveparticles. Dull superabrasive particles may only intermittently cut theCMP pad surface, thus decreasing the density of asperities thereon.

In another aspect, the pressure and/or RPM may be increased when the CMPpad surface exhibits a decrease in average asperity depth. As thesuperabrasive particles begin to dull they no longer have sharp tips andedges that allow deep asperities to be cut. By increasing the cuttingpressure and/or RPM, the superabrasive particles will be pressed furtherinto the CMP pad surface and more evenly distributed, thus cuttingdeeper asperities that can hold more slurry.

In yet another aspect, the pressure and/or RPM may be increased when theCMP pad surface exhibits a decrease in average asperity width. As hasbeen described, as the superabrasive particles wear, their tips andedges become rounded and smooth. As the tips and edges wear off, theseparticles begin to cut wider asperities that reflect their now-wornsurfaces. Though increasing pressure and/or RPM may not decrease thewidth of the asperities back to pre-dull levels, it may allow deeperasperities to be cut, thus allowing retention of larger amounts ofslurry during polishing.

In a further aspect, the pressure and/or RPM may be increased when theCMP pad surface exhibits a decrease in average asperity length. As thetips and edges of the superabrasive particles wear, they have a tendencyto locally deform the surface of the CMP pad rather than cut asperitiesin it. As such, worn superabrasive particles tend to intermittently cutand deflect the surface, thus creating asperities with a decreasedaverage length. By increasing the downward pressure and/or RPM of thesuperabrasive particles, cutting can be prolonged, thus increasing theaverage length of the asperities in the pad surface.

Additionally, if the CMP pad surface asperities are deeper, wider,longer, or denser that what is required to hold the slurry, the pressureand/or RPM between the pad and the dresser may be decreased to slow downthe wear of the superabrasive particles, and thus extend the servicelife of the dresser.

Another method of determining the extent of superabrasive particle wearmay include an examination of at least a portion of the plurality ofsuperabrasive particles disposed on the dresser. Though directexamination of the condition of the superabrasive particles may entailremoving the dresser from the surface of the CMP pad, such anexamination may provide a more accurate assessment of the surface of thedresser than merely observing the cutting pattern of the tool. Followingsuch an assessment, the pressure and/or RPM applied by the dresser tothe surface of the CMP pad can be varied relative to the amount ofsuperabrasive particle wear observed.

Yet another method of determining the extent of superabrasive particlewear may include an estimation of superabrasive particle wear based ondresser use. Over time, one skilled in the art may be able to estimatesuperabrasive particle wear patterns based on wear patterns of previousCMP pad dressers. In many situations this estimation method may prove tobe beneficial due to its cost effective nature. Varying the pressureand/or RPM between the CMP pad dresser and the surface of the pad due toestimated superabrasive particle wear patterns precludes the need forstopping the polishing process to examine the surface of the CMP pad orthe condition of the superabrasive particles in the dresser.

Various methods of altering the pressure and/or RPM between the CMP paddresser and the pad surface are contemplated, and all would beconsidered to be within the scope of the present invention. For example,in one aspect varying the pressure and/or RPM may include a manualadjustment. When it is determined that the superabrasive particles onthe dresser have become worn, the pressure and/or RPM can be variedmanually to take into account and thus counteract such a worn condition.Such a manual change may occur as a result of observing the asperitiesin the pad surface, examining the condition of the superabrasiveparticles on the dresser, or estimating the amount of wear based ondresser use.

It is also contemplated that the pressure and/or RPM between the CMP paddresser and the pad surface may be varied automatically. Numerousautomatic methods are possible, including automatic variations as aresult of observations of superabrasive particle wear, estimations ofsuperabrasive particle wear, anticipation of superabrasive particlewear, etc. This may include notification of the observed wear of thesuperabrasive particles followed by an automatic increase.Alternatively, the pressure and/or RPM may be increased as the dresserhas been utilized to a point that an estimated level of superabrasiveparticle wear has been achieved. In one aspect, a computer control isutilized to automatically vary the pressure and/or RPM. Such a computercontrol may allow the increase of pressure and/or RPM over a largenumber of polished wafers. As such, in one aspect the pressure and/orRPM can be initially increased by very small increments when thesuperabrasive particles are sharp, and subsequently increased by largeramounts as they begin to dull. For example, the pressure and/or RPM canbe increased by about 1% for the first 500 wafers polished, 5% for thenext 500 wafers polished, 10% for the next 500 wafers polished, etc. Inanother aspect, the computer control can increase the amount of pressureand/or RPM for each successive wafer in order to more effectively extendthe service life of the dresser.

Other pressure and/or RPM increasing methods may include situationswhere the pressure and/or RPM is increased without regard to actual orestimated wear. In one aspect, the pressure and/or RPM between the padand the dresser may be gradually increased over time as the dresser isused. For example, in one aspect the pressure and/or RPM between the padand the dresser may be increased following a dressing operation. Inthose cases where the dresser is intermittently dressing the pad whilethe pad is polishing a wafer, the pressure and/or RPM may be increasedfollowing one or more dressing operations during polishing. The pressureand/or RPM may also be increased following each dressing operation ofthe dresser. In another aspect, the pressure and/or RPM may be increasedduring a dressing operation. This would entail increasing the pressureand/or RPM between the pad and the dresser while the dresser is incontact with and is actively dressing the pad. In yet another aspect,the pressure and/or RPM between the pad and the dresser is increasedfollowing completion of polishing of a wafer. Pressure and/or RPM may beincreased following the polishing of a set number of wafers, or may beincreased following the polishing of each wafer.

Various non-limiting examples of gradually increasing pressure and/orRPM may include linear increases, non-linear increases, exponential orlogarithmic increases, stepwise increases, etc. This method provides thebenefit of not requiring an examination or estimation step to ascertainsuperabrasive particle wear. Additionally, pressure and/or RPM may beincreased in anticipation of a worn condition. It may be the case thatthe service life of a CMP pad dresser may be further increased byvarying pressure and/or RPM in anticipation of rather than as a resultof superabrasive particle wear.

Various methods of varying pressure and/or RPM may also include theautomatic detection of phenomenon that may be indicative of a givenlevel of superabrasive particle wear, as discussed above. For example,as the superabrasive particles on the dresser begin to become dull androunded, friction between the dresser and the pad may increase. In oneaspect, such an increase in friction due to superabrasive particle wearmay be detected, and the pressure and/or RPM between the pad and thedresser may be increased in order to compensate.

In another embodiment, a method for extending the service life of achemical mechanical polishing pad dresser used to dress a chemicalmechanical polishing pad, where the dresser has a substrate and aplurality of superabrasive particles disposed thereon, can comprisedressing the chemical mechanical polishing pad with the dresser;vibrating, in a direction substantially parallel to a working surface ofthe pad, a member selected from the pad, the dresser, a wafer beingpolished by the pad, or any combination thereof, to minimize amechanical stress on the pad, dresser, wafer, or combination thereof;and varying the pressure and RPM between the pad and the dresser,including gradually increasing the pressure and/or the RPM between thepad and the dresser in a non-linear manner over time as the dresser isused, such that the dresser life is extended, wherein the pressure andthe RPM is increased when the chemical mechanical polishing pad surfaceexhibits wear.

In addition to varying pressure and/or RPM, the inventors have foundthat certain vibrations imparted to abrasive particles of a CMP dresserduring routine conditioning cycles can reduce the drag coefficientimparted on the superabrasive particles which may result in manybenefits to the CMP pad and dresser itself. For example, a reduced dragcoefficient may create CMP pad asperities having substantially uniformheights and CMP pad troughs or grooves having substantially uniformdepths. Additionally, the inventors have discovered that CMP padspossessing such properties can have more predictable polishing rates andcan promote higher quality polished wafers. Other benefits derived fromreduced drag coefficients are CMP pads having an extended service lifeand reduced wear on the superabrasive particles.

Vibrating the CMP apparatus (including any portion of the CMP pad, CMPpad dresser, or wafer), also reduces stick-slip of the materials. Thatis to say that vibrating the pad, dresser, and/or wafer reduces thedirect and potentially harmful contact that they have upon contactingeach other. Often, materials have a tendency to stick on each other (dueto the forces of friction) and then slip. In most applications ofmovement, this effect is not detrimental, damaging or even a hindrance,however, in dealing with materials with such a tight tolerance forthickness and surface variance, these stick-slip effects can be verydamaging. Including a vibrational aspect to CMP allows for moreefficient polishing and dressing. There will be less tearing anddeformation in both processes due to the reduced stick-slip. Theefficiency of the process is further improved by the vibrating in thatthe consumption of slurry, if used at all, can be reduced. The vibratingallows for the slurry particles to be used many more times before it isdislodged, again as a result of the reduced stick-slip.

The vibrational movements of the particles have been found to beeffective at improving the wear on the particles as well as improvingthe rejuvenated properties of a CMP pad. Functionally, the vibrationscan reduce the amount of pad material and frequency that the materialcomes into contact with the superabrasive particles. As thesuperabrasive particles vibrate at ultrasonic rates and cut into the CMPpad, a consistent portion of material can be displaced on both sides ofthe superabrasive particles thereby creating uniform heights inasperities to promote uniform polishing of wafers. Additionally, aminimized drag coefficient can reduce the wear on and extend the servicelife of the superabrasive particles by limiting the amount of contactwith the CMP pad material during a grooming process.

Accordingly, a method that reduces drag coefficients on CMP padparticles can create CMP pad asperities having substantially uniformheights and troughs having uniform depths. The uniform heights anddepths can be created by the specific vibrations imparted on the dresserparticles. Specifically, the particles can vibrate in either a lateral,circular, elliptical, or any random motion that is substantiallyparallel to the working surface of the CMP pad. In one aspect of thepresent invention, the particles are vibrated laterally, i.e. side toside, such that the dragging is reduced since the amount of padcontacted is reduced. It has also been discovered that the amount ofdrag is significantly reduced when the particles vibrate substantiallyparallel to the working surface of the CMP pad, instead of vibratingperpendicularly or vertically to the working surface of the pad. As aresult, many benefits to the CMP pad and dresser can be obtained, suchas uniform and minimal asperity sizes.

Vibrators, or a source of vibration, may be located at various locationson the CMP apparatus. The vibrator may be attached to the CMP pad at anylocation that can produce oscillations in a direction substantiallyparallel to the working surface of the CMP pad. Examples includeattachment or coupling to the side or periphery of the CMP pad,attachment to any portion of the underside of the CMP pad (i.e. the padsubstrate that is the opposite side of the working surface, attachmentto the side of the CMP pad, inclusion in any feature attached to the CMPpad (i.e. shafts, backings), etc. Likewise, attachments to the CMP paddresser may be to the side of the substrate, periphery of the workingsurface, on the underside of the dresser, in a shaft or otherencasement, etc. Attachment to the wafer is possible through theinstrument attached to the wafer (such as the retainer ring), or to thewafer directly, via any method known in the art.

In the present invention, the CMP pad dresser or CMP pad can have atleast one vibrator coupled to the dresser at a location that vibratesthe dresser in a direction substantially parallel to a working surfaceof the CMP pad with which the CMP pad dresser is engaged. One vibratorcan be coupled to the CMP pad dresser, although multiple vibrators maybe needed to obtain the proper vibration of the superabrasive particles.With the use of a vibrator, the vibrator can impart vibrations on thesuperabrasive particles of the CMP pad dresser, which in turn can reducethe drag coefficient. The vibrator may be of any type capable ofproducing the herein outlined beneficial vibrations. Anyelectro/mechanical actuation system may be utilized to produce thedesired vibrations. In accordance with one aspect of the presentinvention, the vibrator may be an ultrasonic transducer comprised of apiezoelectric material. Alternatively, the vibrator may be a solenoidwith coils of conducting wire. These embodiments are in no wiselimiting; other vibrator means may be employed. In another embodiment,multiple vibrators such as ultrasonic transducers, solenoids, orcombinations thereof, can be coupled to the dresser at locations thatvibrate the dresser and the particles in a direction that issubstantially parallel to the working surface of the CMP pad. Thevibration may be directionally focused or diffused. Additionally, thevibrations may be amplified by an amplifier or dampened with a dampingplate such as an acrylic board. In some aspects, the vibration may bedirectionally controlled, including back and forth directions, circular,square, figure eight, rectangle, triangle, and other simple or complexdirectional vibration movements and patterns may be used.

More than one vibrator may be used. In one embodiment, the vibrators maybe designed to produce a symmetrical vibration, thus achievingresonance. In another embodiment, the vibrations from multiple sourcescan be asymmetrical, thus causing variation across the pad and/or wafer.This can be favorable in the case where a portion of the pad is leastconsumed, thus the vibrations may be intensified in that area so thatthe pad profile will have the effect of being flat. Such a design canbalance pad usage and is useful to achieve a more uniform thickness orflatter surface of the wafer.

The frequency of the present invention may range from about 1 KHz toabout 1000 KHz. The power range may be from about 1 W to about 1000 W.As previously mentioned, the vibrations imparted on the superabrasiveparticles of the CMP pad dresser originate from a vibrator or avibration means such as piezoelectric transducers. In use, the CMP paddresser or CMP pad can vibrate in either a lateral, circular,elliptical, or random motion substantially parallel to the workingsurface of the CMP pad in addition to the afore mentioned directions.Alternatively, the vibration may be completely in a direction parallelto the working surface of the CMP pad. The piezoelectric transducersshould be suitable to vibrate the particles at ultrasonic frequenciesgreater than 15 kHz. Typically, frequencies higher than those audible tothe human ear, i.e. more than about 15,000 cycles per second, areconsidered ultrasonic. In one embodiment the vibrator can oscillate theparticles at a frequency of about 20 kHz.

In a further embodiment, the ultrasonic vibrations may greatly improvethe process by dispersing slurry particles on the CMP pad. Slurryparticles, either those present as part of a slurry to aid in the CMPprocess, or particles that have been removed from the objects beingpolished, have a tendency to adversely affect the polishing process.These particles may build up on portions of the CMP pad and scratch theobject being polished, e.g. the wafer. Ultrasonic vibrations candisperse the slurry particles and provide a mechanism for more efficientremoval of glazed materials and debris.

In another embodiment of the present invention, the vibrator can beadjusted to control the vibrational movements of the superabrasiveparticles, as well as the drag coefficient of each particle to obtain anoptimal polishing experience. Controlling or adjusting either vibrationfrequency, amplitude or both of the ultrasonic wavelengths can alter thepolishing performance for a given CMP pad dresser. Specifically, higherfrequencies can produce asperities having higher ridges and/or deepertroughs. Alternatively, increasing the amplitude of the ultrasonicvibrations can also affect the asperity sizes, which can produceasperities that allow for more slurry to penetrate in to the pad surfacethereby increasing the overall polishing performance of the system. Inreality, controlling the vibrational frequency and amplitude alters thedrag coefficient on each grooming superabrasive particle which altersthe size of each asperity. Such an embodiment can be conducive forobtaining optimal polishing performance for various applications. Forexample, increasing the frequency and reducing the amplitude may beneeded for optimal polishing of oxide layers on a more brittle wafer. Onthe other hand, reducing the frequency and increasing the amplitude ofthe vibrations can be more effective at polishing metal layers (e.g.copper circuit) on a wafer. Further, controlling the vibrationalproperties may be necessary when other polyurethane-type materials areused form a CMP pad that reacts differently under the pad dressingprocess.

In one embodiment, the vibrating can be continuous or interrupted.Additionally, the vibrating can be performed as part of a plurality ofsteps, or a program wherein different vibrational parameters areselected at specific times during the polishing process. The vibrationalparameters include, without limitation, frequency, amplitude, andsource. In general, large amplitude can cause faster removal but withhigher likelihood of damage, while high frequency at low amplitude canpolish slower but with better finish. Therefore, it logically followsthat a polishing program that starts at a large amplitude and thenchanges to a high frequency low amplitude vibration can be verybeneficial in producing a polished material in faster time, and withbetter finish than polishing with at a single set of vibrationalparameters. The program can change continuously, e.g. changing from alarge amplitude to a slow amplitude over time, or there may be differentand distinct stages, e.g. changing from a large amplitude immediately toa slow amplitude, either with or without a time pause between changing.

For example, with the case of removal of copper, the CMP process can becontrolled for fast removal initially by high amplitude low frequencywhile the copper surface is rough and then it can be ramped down to highfrequency low amplitude when the end point is approaching such as whenthe barrier layer of tantalum nitride is exposed beneath the copperlayer. Furthermore, the vibrational parameters can be modified inaccordance to tune to specific conditions, such as addition of slurry,slurry viscosity, new wafer, different wafer-types, new or different padconditioners or dressers, and other variables that reflect changing padconditions. In another embodiment, the vibrations may cause thetemperature of at least a portion of the CMP pad to increase by at leastabout 5° C. In another embodiment, the temperature may increase by atleast about 20° C. Additionally, when the present methods using varyingpressure, RPM, and vibration can provide a synergistic effect inextending the service life of a chemical mechanical polishing paddresser.

It is to be understood that the above-described compositions and methodsare only illustrative of preferred embodiments of the present invention.Numerous modifications and alternative arrangements may be devised bythose skilled in the art without departing from the spirit and scope ofthe present invention and the appended claims are intended to cover suchmodifications and arrangements.

What is claimed is:
 1. A method for extending the service life of achemical mechanical polishing pad dresser used to dress a chemicalmechanical polishing pad, the dresser having a substrate and a pluralityof superabrasive particles disposed thereon, comprising: dressing thechemical mechanical polishing pad with the dresser; determiningsuperabrasive particle wear by measuring a mechanical property of thepad, dresser, or combination thereof; and responding to the mechanicalproperty measurement by varying pressure and RPM between the pad and thedresser in relation to the superabrasive particle wear in order toextend dresser life.
 2. The method of claim 1, wherein the measuredmechanical property is selected from the group consisting of frictionalforce, acoustic emission, temperature, pad reflectivity, padflexibility, pad elasticity, and combinations thereof.
 3. The method ofclaim 1, wherein varying the pressure and RPM includes graduallyincreasing the pressure and RPM between the pad and the dresser.
 4. Themethod of claim 3, wherein the gradual increase for the pressure and/orRPM over time is a nonlinear exponential increase.
 5. The method ofclaim 1, wherein varying the pressure and RPM includes automaticallyincreasing the pressure in response to increased superabrasive particlewear.
 6. The method of claim 1, further comprising vibrating, in adirection substantially parallel to a working surface of the pad, amember selected from the pad, the dresser, a wafer being polished by thepad, or any combination thereof, to minimize a mechanical stress on thepad, dresser, wafer, or combination thereof.
 7. The method of claim 6,wherein the dresser vibrates in a lateral, circular, elliptical, orrandom motion substantially parallel to the working surface of the pad.8. The method of claim 6, wherein the vibrating is only in a directionparallel to a working surface of the pad.
 9. The method of claim 6,wherein the vibrating is at an ultrasonic frequency greater than 15 kHz.10. The method of claim 6, wherein the vibrating is continuous.
 11. Themethod of claim 6, wherein the vibrating is diffused.
 12. The method ofclaim 1, wherein pressure and RPM is increased when the chemicalmechanical polishing pad surface exhibits a decrease in average asperitydensity, average asperity depth, average asperity width, averageasperity length, or combination thereof.
 13. A method for extending theservice life of a chemical mechanical polishing pad dresser used todress a chemical mechanical polishing pad, the dresser having asubstrate and a plurality of superabrasive particles disposed thereon,comprising: dressing the chemical mechanical polishing pad with thedresser; vibrating, in a direction substantially parallel to a workingsurface of the pad, a member selected from the pad, the dresser, a waferbeing polished, by the pad, or any combination thereof, to minimize amechanical stress on the pad, dresser, wafer, or combination thereof;and varying the pressure and RPM between the pad and the dresser,including gradually increasing the pressure and/or the RPM between thepad and the dresser in a non-linear manner over time as the dresser isused, such that the dresser life is extended, wherein the pressure andthe RPM is increased when the chemical mechanical polishing pad surfaceexhibits wear.
 14. The method of claim 13, further comprisingdetermining superabrasive particle wear.
 15. The method of claim 14,wherein determining superabrasive particle wear includes measuring amechanical property of the pad, dresser, or combination thereof.
 16. Themethod of claim 15, wherein the measured mechanical property is selectedfrom the group consisting of factional force, acoustic emission,temperature, pad reflectivity, pad flexibility, pad elasticity, andcombinations thereof.
 17. The method of claim 16, wherein determiningsuperabrasive particle wear further includes examination of a dressedchemical mechanical polishing pad surface.
 18. The method of claim 17,wherein pressure and RPM is increased when the chemical mechanicalpolishing pad surface exhibits a decrease in average asperity density,average asperity depth, average asperity width, average asperity length,or combination thereof.
 19. The method of claim 14, wherein determiningsuperabrasive particle wear further includes an estimation ofsuperabrasive particle wear based on dresser use.
 20. The method ofclaim 13, wherein the vibrating is only in a direction parallel to aworking surface of the pad at an ultrasonic frequency greater than 15kHz.